Role of If (Funny Current) on Biological Pacemaker – Insight From a Ventricular Model

Yacong Li1, Kuanquan Wang1, Qince Li1, Xiangyun Bai1, Henggui Zhang2
1Harbin Institute of Technology, 2University of Manchester


Aims: Biological pacemaker (biopacemaker), generated by turning non-pacemaking cardiac myocytes into automaticity has been proposed to be a promising alternative to electrical pacemaker for treating patients with impaired native cardiac pacemaker. It has been shown that overexpressing the hyperpolarization-activated funny channel current (If) can induce automatic pacing activities in ventricular myocytes (VMs). However, the role of If expression in generating automaticity in VMs has not been fully understood. In this study, we implemented a computational approach to investigate mechanism by which overexpression of If helps VMs to become biopacemakers. Methods: The TP06 model for the electrical action potential (AP) of the human VMs was modified by incorporating If formulation. The channel conductance If (Gf) was changed systematically from 0 to 1 nS/pF. Results: When Gf ≥ 0.09 nS/pF, the VMs showed spontaneous pacing activities. With an increase of Gf, the cycle length (the time interval between two consecutive APs) was gradually shortened. During the time course of spontaneous APs, changes in the intracellular ion concentrations occurred due to the secondary effect of If, leading to accumulation of intracellular calcium concentration ([Ca2+]i) as well as the intracellular sodium concentration ([Na+]i). However, a decrease in the intracellular potassium concentration ([K+]i) was observed. By clamping [Na+]i and [K+]i to a constant level (10.56 and 134.8 mM respectively), a fast and stable spontaneous pacemaking activity was observed. Conclusion: Overexpressing If in VMs is able to produce automatic rhythms in VMs. With the increase of If, the pacing ability becomes stronger, implicating the important role of If magnitude in biopacemaker. To generate a stable and optimized pacemaker one may also need to consider the role of dynamical behaviours of [Na+]i and [K+]i. This study provides new insights into the mechanism of creating biopacemakers using If overexpression.